Breast cancer is the leading cancer diagnosed among woman in the US and is the second leading cause of cancer deaths. Adjuvant chemotherapy has been proven to decrease the risks of relapse and mortality from breast cancer. However, older adults are at increased risk for chemotherapy toxicity, including an increased risk of treatment-related mortality. At present, there is only preliminary evidence regarding which brain structures and functions are affected by chemotherapy and toxicity in breast cancer patients. However, this prior research did not specifically study older women. Thus, there is a need to establish a more sensitive test that has reproducible biomarkers, to identify the older breast cancer patients who are at higher risk for chemotherapy toxicity Our long term goal is to identify highly sensitive and reproducible brain MRI biomarkers that are associated with chemotherapy toxicity in aging cancer patients. Toward that goal, the objective of this study is to define the changes that occur on brain MRI and to determine the relationship between brain MRI changes and chemotherapy toxicity in older adults with breast cancer. We aim to 1) define structural and functional changes that occur on brain MRI of older women with breast cancer receiving adjuvant chemotherapy and; 2) determine the relationship between the severity of structural and functional changes on brain MRI and chemotherapy toxicity. We expect that the severity of structural and functional changes to the brain MRI in our patients will correlate with the severity of chemotherapy toxicity. The proposed study is significant because it focuses on the unknown relationship between brain MRI changes and chemotherapy toxicity in older women with breast cancer. It is innovative because it proposes advanced MRI techniques to study and identify the novel potential biomarkers for chemotherapy toxicity in older adults with breast cancer. It will have a positive impact by helping to clarify the underlying pathophysiology of cognitive decline caused by chemotherapy toxicity. The data generated from this pilot study will also help to serve as a foundation for future large scale studies of cognition and chemotherapy in older adults.